Wesley g



Patented Dec. 2, 1924.

UNITED STATES PATENT OFFICE.

WESLEY Gr. NICHOLS, OF CHICAGO HEIGHTS, ILLINOIS, ASSIGNOR TO AMERICAN MANGANESE STEEL COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF MAINE.

HEAT TREATMENT OF MANGANESE STEEL.

No Drawing.

To all whom it may concern:

Be it known that I, IVEsLnr Gr. Nrcnons, a citizen of the United States, residing at Chicago Heights, in the county of Cool: and State of Illinois, have invented certain new and useful Improvements in the Heat Treatment of Manganese Steel, of which the following is a specification.

This invention relates to a method of heat treating manganese steel castings, and has for its primary object to provide a method of procedure which will greately increase the quantity of castings that can be treated in a given furnace within a given period of time without injury to the castings.

In the heat treatment of manganese steel castings in gas, coal, or oil fired furnaces the practice has been to establish approximate equilibrium of temperature between the castings and furnace at the time of charging the furnace, this being accomplished by either allowing the furnace to cool down to about the temperature of the castings, or holding the castings in the molds where they are protected from atmospheric changes until the furnace is drawn and ready to be recharged, and then shaking the castings out of'the molds at approximately the furnace temperature, breaking the heads and gates from the castings, and charging the cast ings as quickly as practicable into the furnace, which proceeding involves considerably more labor than the prices warrant, while the high temperatnrcs ofthe castings which the workmen have to contend with prevent cleaning the castings of sand sufliciently to admit of proper treatment. It has never been considered practicable to charge cold castings into a hot furnace because the flame or gases in furnaces of the types named have been too severe and too unevenly distributed. The light sections would take the heat long before the heavy sections did, attaining in many cases a red heat or from 1200 to 1 100 F. before the heavy sections reached as much as 700 to 800 F. This would cause excessive expansion of the light sections accompanied by a tendency to pull away from the heavy Serial No. 621,461.

sections, or to check, or otherwise render the castings unserviceable.

I have found that by the procedure of the present invention and the use of an electric furnace of the resistance type, manganese steel castings may be charged into the furnace at atmospheric temperature even though the furnace has a temperature of from 1100 to 1400 F. or even higher. without any damage being done to the castings, thereby saving the time heretofore consumed in cooling down the furnace to what was supposed to be a safe temperature to receive the cold castings, and saving the expense of the proceeding incident to introducing the castings hot from the molds already alluded to, and avoiding the disadvantage of introducing into the heating furnace castings insufficiently cleaned of sand.

In carrying out the invention, since time is unavoidably consumed in the original heating of the furnace to working temperature after a shut-down, the general practice has been to insert the first charge of castings into the furnace while the latter is cold, and then developing the heat. This involves no special problem since the furnace starts at approximately the temperature of the castings, or at atmospheric ten'iperatnre. Innnw diately upon removal of this load. a succeeding load is ready for introductimi into the furnace. At this time the tein ierature of the furnace will be about 1300 h. in consequence of some loss incident to the opening of the furnace and removal of the charge in which the heating has been completed. The new load is introduced into the furnace at this temperature of, say 1300 F. and the furnace door is immediately closed, but the current which was interrupted at the end of the previous treatment is left off for a period of fifteen to thirty minutes after the introduction of this second charge and the closing of the furnace. At the end of this last-named period the temperature of the furnace will be found to have dropped, in consequence of absorption of heat by the castings, to from 1075 to 1125 F. Current is now supplied to the resistance elements of the furnace and heat is developed thereby, but at a rate which is not materially in excess of the power of the castings to absorb the heat, so that at the end of the first hour of application of power the temperature will be found not to have increased owing to continued absorption of heat by the charge of castings; it may have decreased as much as from 15 to 35 F. At the end of the, second hour the ten' perature will still be substantially about. that at which it stood when the current was applied, but after the second hour temperature will be observed to gradually increase until it attains the upper 'criticalpointbeyond whichit should not be permitted to go in the treatment of manganese castings. Having attained the highest temperature, the current is regulated to hold the furnace at such temperature for the requisite period of time to insure complete heat treatment, when the current will be shut off, the furnace opened, the finished charge removed,and a third charge immediately introduced with a repetition of the cycle of conditions already eninnerate-d. By proceeding in this manner, great economy in current consumption and time required for each heat treatment, and consequentincrease of furnace capacity for a given expenditure of a current, result. Moreover, the life of the furnace lining as well as other parts of the furnace is prolonged by the elimination of repeated cooling and heating of the furnace.

The procedure above outlined and the results mentioned are not practicable with furnaces of the gas, coal, or oil-fired types because in, such furnaces the heat sourceis generally located in one part of the furnace and the heating medium is forced in under pres sure of'air, with the result that the wall opposite the heat source is at higher temperature than the wall adjacent thereto; moreover, the roof develops a higher temperature than the bottom of t io furnace, with the result that certain castings or parts of castings to be heated attain a very high temperature while other castings or parts are eo n 'iarat'ively cool, which condition. causes undue strains in the pulling away of the light sections from the heavy sections. VVith the electric furnace, each and every part of the furnace is at the same temperature, and even after the current is turned on the heat is so diffused throughout the furnace that there is no chance for any part to attain a higher temperature than the other parts, and it is impossible to overheat any particular part of the furnace. This is evidenced by the fact that the furnace temperature at the end of two hoursis found to be' approximately the same as it was at the beginning of the operation. With this uniformity of furnace temperature, each portion of the castings absorb heat uniformly.

By the procedure of the present invention it is possible to heat treat manganese steel castings of any size and variation of section with safety and without danger of spoiling the castings. It is not necessary to allow the heat treating furnace to cool to the temperature of the castings before introducing the latter; castings at atmospheric temperature as wellas castings having a very high degree of heat can be charged into the same furnace without anyinjuryto the cooler castings; and the furnace can have a relatively high temperature, evcnas high as 1600 F., at the time of charging the castings without endangering the latten As a result of these conditions, all castings can. be treated in a given length of time andat a lower cost of power, large furnace equipment can be eliminated, and the quantity of castings scrapped on account of furnace cracks can be greatly reduced.

I claim:

1. The improvement in the art of heat treating man anese steelcastings, which consists in intro ucing castings to be heat treated, while atlow temperature, into a furnace standing at relatively high temperature but with the interruption of the heat source, permitting the temperature of the furnace to fall for a timewhile the castings absorb the heat, and thereafter generating heat in the furnace and raising the temperature to that re quired for completing heat treatment.

2. The improvement in the art of heat treating manganese steel castings, which consists in introducing castings to be treated into a furnace standing atrelatively. high temperature but with interruption of heat source, maintaining this condition until the castings absorb a substantial quantity of heat stored in the furnace, then resuming genera.- tion of heat in the furnace at a rate approximately commensuratewith heat absorption of the castings, and slowly bringing the castings to the upper limit required to complete their treatment.

3.-The improved method. of heat treating castings, which consists in introducing the castings to betreated into a furnace at the high temperature at which. the furnace stands following withdrawal of a completed charge of castings but with interruption of heat source, continuing the interruption of heat until the newlyintroduced castings have absorbed a substantial quantity of heat stored in the furnace, then renewing the heat source and generating heat while the same is being additlonally'absorbed by the castings, and ultimatelyv attaining and maintaining the upper limit of heat required tocomplete the treatment.

4. The improvedmethod of heat treating manganese steel castings, which consists in interrupting the heat source. of an electric furnace, removing a completely heat treated charge of castings from the furnace, immediately introducing a new charge of manganese steel castings into the furnace With the heat source still interrupted, continuing the in terruption of heat source until the castings have absorbed a substantial quantity of heat from the furnace, then renewing the generation of heat at the source at a rate commensurate with the heat absorption of the castings until necessary temperature is attained for completing the heat treatment, and maintaining the last-named temperature until the treatment is complete.

Signed at Chicago, Illinois, this 18th day of February, 1923.

WESLEY G. NICHOLS. 

